Corona device

ABSTRACT

A corona discharge element disclosed is made in the form of a gear rack in which the end of each gear tooth is flat with four sharp corners for corona emission. Also disclosed is an assembly of a plurality of such elements embedded in a dielectric plate to provide an efficient uniform corona discharge over a predetermined area.

l tent 1 @et. 16, E973 CORONA-DEVIE Inventor: Heh-Sen Lin, Burlington, Mass.

FIST "A igieez LFE Corporation, WaItharn, Mass Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Attorney-Richard J. Donahue [5 7] ABSTRACT A corona discharge element disclosed is made in the form of a gear rack in which the end of each gear tooth is flat with four sharp corners for corona emission. Also disclosed is an assembly of a plurality of such elements embedded in a dielectric plate to provide an efficient uniform corona discharge over a predetermined area.

4 Claims, 3 Drawing Figures C II ll ll ll II H II II II II II II II II II II II II II II IFII II ll 11 I! II II CllllllllllllllllllllllllllllllllllllllIIIHIIHIIHHIII) L lHlIllI llll llJl IHHIII Il llllllllll I! ll Illl lllllllll I] D IIIIIIIIIIIIIHIIIIIIlllllllillllllllIlllllllllllllllll 3 u II II n n n II II n n n u n u n n n n n u u 11'" H "mm C lllllllllllllllllllllllllllllllllllllI-IIIIIIIHHHIIIII 3 LII IIIIIIIHIIIIIllllllllllllllllIIIIIIIHIIIIHIIIIHHD CORONA DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is related to corona discharge devices and particularly to such devices used to treat nonconductive articles.

2. Description of the Prior Art Treatment with a corona discharge has been found to render many plastic and certain other materials more receptive to coatings, and to otherwise alter the surface and interior characteristics of the materials for a variety of industrial applications. Disclosure of a system for corona treatment of plastic materials has been made by Antokal in U. S. Pat. No. 3,192,385.

Antokal discloses corona treatment of a continuous web of flat material. It is frequently desirable to corona-treat preformed articles such as dishes and various containers. While many available corona devices, such as that of Antokal, operate well over a short distance; for example, one-half inch, a greater distance is necessary in corona treatment of preformed articles. Corona devices that have been used to provide a corona across greater distances have usually been single-pointed probes that provide no uniform corona, except in a relatively limited area. Devices for providing uniform corona have generally been designed to operate against a flat surface over a short distance. Examples of such devices are found in U. S. Pat. No. 3,294,971 to Von der Heide and U. S. Pat. No. 3,691,373to Compton et al. In corona treatment of preformed articles, it has also been found desirable to provide a uniform corona discharge over an extended area; for example, a squarefoot or more. While much of the prior art discloses a plurality of the electrodes, this plurality is generally an in-line repetition; for example, a plurality of needles. It is believed that there has been no real attempt in the past to provide uniform corona over an extended two dimensional area.

SUMMARY OF THE INVENTION In accordance with the present invention, a corona discharge element is provided in the form of a gear rack such that the end of each tooth of the gear has four sharp corners, each adapted to emit corona discharge. A plurality of these elements positioned in parallel on a dielectric backingwith a properly selected interelement spacing have been found to produce corona discharge over any desired extended area and to be suitable for providing a uniform emission over a spacing distance from an opposed conductive surface of at least one and one-half inches. It has also been found, in accordance with the invention, that imbedding nonemitting portions of the electrode elements in the dielectric backing so as to minimize exposed conducting material improves the efficiency of the system. Thus, it is an objective of the invention to provide a novel corona element in the general form of a gear rack.

It is the further objective of the invention to provide acorona electrode having a plurality of projections, each projection having a plurality of sharp corners.

It is a further objective of the invention to provide an array of corona discharge elements comprising a plu-v rality of elements arranged on a dielectric support. It is a further objective of the invention to provide a corona discharge array arranged to produce a uniform corona discharge over an area in excess of one square foot.

Further objectives and features of the invention will become apparent upon reading the following description together with the drawing.

BRIEF DESCRIPTION OF THE DRAWING:

DESCRIPTION OF THE PREFERRED EMBODIMENT The corona electrode array for providing a uniform corona discharge over a large area is depicted in FIG. 1. A dielectric sheet 10 which may be made of any of the many available self-supporting, and electrically insulating plastics, supports a plurality of corona discharge electrodes 11. FIG. 1 is depicted at approximately one-fourth scale of an actual array such that dielectric sheet 10 is approximately a little over one foot by two feet. Corona discharge elements 11 made in the form of gear racks, each having approximately teeth 12 and being about one foot in length, are secured to plastic sheet 10 spaced about two inches on center so that there are thirteen elements 11 in the array. Due to the scale, teeth 12 have been depicted only symbolically in FIG. 1. The symbolic markings are not indicative of the true number of teeth. Elements 11 may be secured to dielectric sheet 10 by some form of adhesive bonding, rivets, screws, or the like.

As depicted in FIG. 2, it has been found preferable that corona elements 11 be recessed in plastic sheet 10 so that only corona emitting teeth 12 of electrodes 11 are exposed. While the reasons are not fully understood, experimentation has indicated that recessing the elements in this manner improves the efficiency of the apparatus. Elements 11 have been used that are 0.250 inches high overall with a tooth height of approximately 0.095 inches. Each element 11 is connected to high terminal 14 of high voltage AC supply 15. Supply 15 is grounded at second terminal 16. In operation an electrically conductive. surface underlying articles to be treated is grounded or otherwise connected toterminal- 1 6. Terminal 14 is suitably connected to one of the fastenings holding each element 11 to sheet 1 0; for example, screw 17.,Connection may be made at screw 17 of one element' ll and from thereto all remaining elements 11 through bus bar 18.

FIG. 3 depicts teeth 12 in greater detail. It will be seenthat ends 20 of teeth 12 are flat, each tooth end having four sharp corners 21,22, 24, and 25. In an exunder the material to be treated of up to one and onehalf inches. The array is then energized with an AC voltage of about to 240 kilovolts in the high frequency band. A uniform corona discharge radiates all material'within one and one-half inches of the corona elements in the array. While not intended to be limiting, it is believed that the dielectric sheet has the combined effect of blocking back radiation, and improving the directivity of forward radiation.

While the invention has been described with relation to a specific embodiment and for a specific purpose, it is applicable for all purposes of both AC and DC corona discharge where improved efficiency and uniformity is desired. Variations in the size of the array, the number and size of the electrode elements, and the number and size of the teeth in the electrode elements are all contemplated as within the scope of the invention and it is intended to cover the invention in accordance with the scope of the following claims.

I claim:

1. A corona discharge array comprising:

a. A dielectric sheet,

b. a plurality of interconnected conductive elements secured to said sheet, each of said elements having the configuration of a gear rack in which the end of each tooth is flat so as to provide four sharp corners to initiate corona emission, and;

0. means for applying high voltage to each of said conductive elements.

2. A corona discharge array according to claim 1 wherein each of said conductive elements is recessed into said dielectric sheet so that only the teeth are exposed.

3. A corona discharge array according to claim 1 wherein each element is spaced a uniform distance from each other element over an area in excess of one square foot to provide a uniform corona discharge over an extended area.

4. A corona discharge array according to claim 1 wherein said dielectric sheet is a solid synthetic resin material. 

1. A corona discharge array comprising: a. A dielectric sheet, b. a plurality of interconnected conductive elements secured to said sheet, each of said elements having the configuration of a gear rack in which the end of each tooth is flat so as to provide four sharp corners to initiate corona emission, and; c. means for applying high voltage to each of said conductive elements.
 2. A corona discharge array according to claim 1 wherein each of said conductive elements is recessed into said dielectric sheet so that only the teeth are exposed.
 3. A corona discharge array according to claim 1 wherein each element is spaced a uniform distance from each other element over an area in excess of one square foot to provide a uniform corona discharge over an extended area.
 4. A corona discharge array according to claim 1 wherein said dielectric sheet is a solid synthetic resin material. 